The invention relates to a method for the pattern repeat presetting of a rotary screen printing machine.
Such a method is known from the published Dutch patent application NL 7906131.
Pattern repeat presetting is important in order to limit loss of material when regulating the machine.
In a multi-colour rotary screen printing machine such as that used, for example, for printing textiles, the colours are printed in succession on a web by means of patterned cylindrical stencils. It is important here that the various colours should be placed in a good position relative to each other on the web. If a new pattern has to be printed, the cylindrical stencils will have to be placed as well as possible in the correct orientation in the machine, following which printing begins. An operator will visually assess the printed result and adjust the machine further in order to achieve the optimum printed result. The setting takes place, inter alia, through varying the orientation of a stencil relative to the other stencils. The latter is the so-called lengthwise pattern repeat setting. Widthwise and diagonal pattern repeat setting can also be carried out.
The earlier mentioned application 7906131 describes a method whereby, for a particular pattern, the setting of the rotary screen printing machine by which a suitable printed result is obtained is saved in a data file. The advantage of this is that when a particular pattern is being reprinted, if the stencils are replaced in the earlier used printing positions, optimum pattern repeat presetting can be achieved by recovering the data saved in the data file and with said data giving the machine the correct pre-setting. Initial losses are greatly reduced as a result.
The disadvantage of this method is that it does not provide any solution for the pattern repeat presetting of a pattern which is to be printed for the first time.
In addition it happens in practice that for a reprint the stencils required for a reprint are placed in the rotary screen printing machine in a different way from that for the first print. Part of the reason for this is the positioning of squeegee and colour feed systems in the printing operation prior to the reprinting. It is then sometimes more practical not to lose unnecessary machine operation time for moving these systems, something which results in great initial losses of material as a result of the re-setting of the machine.
Another reason for placing the stencils in a different order in the machine can be the desire to obtain a different colour scheme. This is obtained by using the same colours for a pattern, but changing the colours of the pattern parts.
Yet another reason for not replacing the stencils in the earlier used printing positions for a reprint can be that in the case of machines which have more printing positions than the number of colours which are being printed the printing positions not used are already prepared for the next printing operation, in order to reduce standstill losses.
The result of this is that the pattern repeat presetting data obtained earlier and saved can no longer be used because the data relate to the advance pattern repeat setting of stencils which are each placed in a specific printing position.
The techniques for patterning cylindrical stencils are being optimized to an increasing extent, so that increasingly more complex patterns with high resolution can be achieved. In addition, there is a demand from the market for patterns with more and more colours (twenty or more), often with the demand for exclusivity. This last demand means that the yardages of printed fabric are becoming smaller, so that the initial losses are relatively high.